ChArUco Calibration Boards: Coded-Marker Targets for Partial-View and Multi-Camera Calibration
A ChArUco board is a checkerboard with coded ArUco markers in its white squares — sub-pixel corners plus a unique ID at each one, so calibration succeeds even when the board is tilted, occluded or only partly in frame. What it is, why it beats a plain checkerboard, the four specs that matter, how to choose a configuration and substrate, how it differs from AprilGrid, and how to order the right target.
AprilGrid Calibration Targets: Coded AprilTag Grids for Kalibr Camera-IMU and Multi-Camera Calibration
An AprilGrid is a grid of individually coded AprilTags used by the Kalibr toolbox for multi-camera and camera-IMU calibration. Unique tag IDs let calibration succeed from partial views and remove the pose-flip ambiguity that affects symmetric checkerboards and circle grids. What it is, why Kalibr recommends it, the tag parameters that matter, how it differs from ChArUco, and how substrate sets the accuracy ceiling.